Pneumocystis carinii (Pc) is a major cause of pneumonia in patients with the acquired immunodeficiency syndrome (AIDS). Progress in meeting the clinical challenges of Pc pneumonia has been slow because of a lack of knowledge about the basic biology of the organism. Our laboratory has had a long-term interest in the immunology, life cycle, and basic biology of Pc. We have recently related the viability and number of Pc organisms in bronchoalveolar fluid (BALF) to clinical disease severity and have shown the ability to detect and characterize Pc antigens in BALF. In the present proposal, we plan to extend this work by further microscopic and antigenic evaluation of BALF and correlation with disease outcome and severity. We will microscopically quantitate organism density and life cycle stage by tinctorial staining techniques; determine viability of organisms by dye exclusion and fluorescent probes; and identify and quantitate developmental stages of Pc by cell imaging analysis. We will determine the antigenic profile of Pc in BALF by immunoblot and lectin blot analysis and then relate these to the clinical disease severity and to patient's serum antibody response. We will define the effects of treatment on these microscopic and antigen features by studying specimens before and on completion of therapy. Knowledge gained from the proposal will enhance our understanding of the effects of therapy and of the pathogenesis of relapse. The quantitation and characterization of organism antigens, detailed morphological and viability studies, and assay of host serological responses may be helpful in assessing prognosis and monitoring therapy.